**4.2 Effect of digestate on soil macroelement content**

One of the main problem of digestate (and other N fertilizer) application is the N leaching. However, Renger & Wessolek (1992) and Knudsen et al. (2006) found that the N leaching was dependent on the use of cover crops. Similar results were reported by Möller & Stinner (2009) who did not find differences in the soil mineral N content among different manuring systems in the case of winter wheat, rye and spelt in autumn, before use of cover crops. That means that the use of cover crops is an appropriate method to avoid N leaching and to compensate for higher N application. From the same experiment, Möller et al. (2008) reported average soil mineral N content in spring. In this case they found significant higher soil mineral N content of the digested slurry treated samples (Table 4).


Table 4. Average soil mineral N content in spring in 0-90 cm with the main crops spelt, rye and spring wheat from 2003-2005 *(Data from Makádi et al., 2007).* a, b, c indexes mean the different values (P<0.05).

Digestate contains high proportion of NH4-N therefore it would be expected to increase NH4-N content of treated soil. However, digestate applied in the fall could easily be nitrified by early spring (Rochette et al., 2004; Loria et al., 2007). This predisposed N loss with occurrence of wet conditions.

a fertilizer, but it could be appropriate as a soil quality amendment (Schleiss and Barth, 2008). Comparing to the other organic materials, the amendment properties rank sequentially as compost ~ digestate > digested sludge >> ingestate, on the bases of OM

Odlare et al. (2008) have not found significant change in the pH after 4-year-long biogas residue application rate. The pH of soils were 5.6 and 5.7 in the control and biogas residue treated samples, respectively. Similar results were reported by Fuchs & Schleiss (2008), because they have found an enhance of soil pH for about ½ unit after harvesting of maize. Because of the alkaline pH of digestates, an increase of the soil pH should be supposed. However, digestate might contain various acidic compounds (e.g. gallic acid). The polycondensation, connection to organic and inorganic colloids and transformation of these acids can have an effect also on the soil chemical properties and finally the decrease of soil pH (Tombácz et al., 1998, 1999), more particularly at the soils with high organic and inorganic colloid contents. Therefore the regular monitoring of soil pH is necessary in case

One of the main problem of digestate (and other N fertilizer) application is the N leaching. However, Renger & Wessolek (1992) and Knudsen et al. (2006) found that the N leaching was dependent on the use of cover crops. Similar results were reported by Möller & Stinner (2009) who did not find differences in the soil mineral N content among different manuring systems in the case of winter wheat, rye and spelt in autumn, before use of cover crops. That means that the use of cover crops is an appropriate method to avoid N leaching and to compensate for higher N application. From the same experiment, Möller et al. (2008) reported average soil mineral N content in spring. In this case they found significant higher

Treatments Soil mineral N (kg N ha-1),

Table 4. Average soil mineral N content in spring in 0-90 cm with the main crops spelt, rye and spring wheat from 2003-2005 *(Data from Makádi et al., 2007).* a, b, c indexes mean the

Digestate contains high proportion of NH4-N therefore it would be expected to increase NH4-N content of treated soil. However, digestate applied in the fall could easily be nitrified by early spring (Rochette et al., 2004; Loria et al., 2007). This predisposed N loss with

0-90 cm soil layer

degradability (Tambone et al., 2010).

**4.1 Effect of digestate on soil pH** 

of long-term digestate application.

Digested slurry + field residues +

different values (P<0.05).

occurrence of wet conditions.

**4.2 Effect of digestate on soil macroelement content** 

soil mineral N content of the digested slurry treated samples (Table 4).

Farmyard manure 65.7 a Undigested slurry 71.1 ab Digested slurry 89.2 c Digested slurry + field residues 81.3 bc

clover/grass and silage maize mixture 83.6 bc

Generally, the digestate application does not cause any significant changes in the total-N and available P content, while the available K content was increased by the application of biogas residue (Olsen et al., 2008). Similar results have found Vágó et al. (2009), who reported the significant increase of 0.01 M dm-3 CaCl2 extractable P content even after 5 L m-2 digestate treatment, while the K content of soil was significantly increased by 10 L m-2 digestate dose only.
